I-405/112th Ave to SE 8th St – Widening


Washington State Department of Transportation

Completion Date



Jacobs Engineering Group


Bellevue, Washington

Delivery Method




Contract Value

$126 million
I-405 South Bellevue

The "I-405 South Bellevue" project widened 4 miles of I-405 between 112th Avenue SE and SE 8th Street to six lanes. Crews built a new northbound lane from 112th Avenue SE to SE 8th Street, a new southbound lane from SE 8th Street to I-90, a new southbound I-405 mainline bridge over I-90 and widened several mainline bridges. In addition, Atkinson repaired pavement in both directions, installed a new ramp meter at 112th Avenue SE, restored the Kelsey Creek wetland, installed new Intelligent Transportation System (ITS) infrastructure, and provided many other improvements.

As part of the widening project, crews tore down the old Wilburton tunnel—a cast-in-place concrete structure supporting an abandoned rail line that restricted traffic flow to four lanes. Due to the high volumes of traffic on this urban transportation corridor (170,000 vehicles per day), the complete closure of the I-405 southbound lanes to demolish the Wilburton tunnel required excellent communication with the public. Atkinson initiated a comprehensive public outreach effort which was vital to the success of this major project milestone.

The public outreach program included a year-long information campaign to local businesses, residents, drivers, the media, and others. Thanks to this concerted effort and comprehensive planning, drivers avoided the area and the impacts on the community were less than expected. Furthermore, crews completed the demolition in only two weekends (instead of the allotted three) by piggybacking other key project activities such as dowel bar retrofitting, diamond grinding, PCC roadway panel replacement, roadway embanking and ramp drainage, and the new southbound I-90 mainline bridge approach tie-in. Completing these activities during the weekend closures eliminated six weeks of nighttime lane closures for concrete rehabilitation and four maintenance of traffic (MOT) alignment shifts.